Switching Mode Power Supply (SMPS) is widely used to convert an input voltage to an output voltage for supplying a load such as a computer or a mobile phone. The output voltage is usually regulated by controlling a duty cycle of a Pulse Width Modulation (PWM) signal that is supplied to a control end of a switch of the SMPS. A multi-phase SMPS comprises a plurality of switching circuits and has a high current carrying ability. Besides, digital PWM signal generator has advantages of strong communication ability and high anti-disruption ability and thus is favored in many applications. Digital control in multi-phase SMPS with fast transient response as well as simple fabrication technology is desired.